Oil system

ABSTRACT

The oil supply device for a change-under-load transmission having a high-pressure circuit and a low-pressure circuit is designed in such a manner that the high-pressure feed line to the consumer devices of the transmission system incorporates an inlet aperture of small size, the low-pressure feed line is connected between the inlet aperture and the consumer device, and the low-pressure feed line can be cut off from the high-pressure feed line by a one-way valve.

[0001] The present invention concerns an oil supply device for the hydraulic transmission control of an automatic transmission and, in particular, a change-under-load transmission with a demand-orientated oil supply system according to the pre-characterizing portion of claim 1, and a method for operating the oil supply device according to the invention.

[0002] According to the state of the prior art, the oil supply of a change-under-load transmission provides, on one hand, for the lubrication and cooling of transmission components and, on the other hand, for their control by hydraulic means.

[0003] For the hydraulic transmission control of a change-under-load transmission, a continuous pump delivery flow is needed so that, at any desired point in time, the gear-shift elements can be filled without delay. During steady state operation, on the other hand, a continuous high pressure of about 15 to 30 bar is needed in order to hold the engaged gears or the variator discs steady, and a smaller delivery flow is required for this.

[0004] For a gear-shift element change, a change-under-load transmission at first needs a large delivery flow, at relatively low pressure, to fill the gear-shift element, and then, during modulation, when the clutch disc is engaged, a higher pressure with a low delivery flow, for example.

[0005] In addition most of the delivery flow is needed for lubrication and cooling of the transmission, and a low pressure of about 2 to 4 bar must be established for this.

[0006] A demand-orientated oil supply system of the prior art usually comprises two separate delivery flows with different pressures, which can be adjusted as necessary, as described for example in the context of patent specification EP 0 550 098 B1. This discloses an oil supply arrangement having a first and a second mechanically driven pump hydraulically coupled to one another in such manner that the control system of the second pump can be regulated, so that the demand-orientated oil supply can be adjusted by the pumps, by means of a regulator device.

[0007] This oil supply has the disadvantage that because of the separate delivery flows or oil circuits and the two mechanically driven pumps, its construction is very elaborate and entails high production and maintenance costs.

[0008] Further, in the context of DE 101 262 60 by the present applicant, it is proposed to provide the necessary, demand-orientated oil supply by means of a transmission oil pump, which delivers oil at high pressure only during a gear shift operation but which, during steady state, is operated at a low pressure level on the order of 3 to 5 bar.

[0009] To produce the required small delivery flow at high pressure at times other than during gear shift operations, as required in order to hold the engaged gears or the variator discs steady, a pressure-volume flow converter is provided, which is integrated into the oil circuit. For a low-pressure delivery flow, this pressure-volume flow converter produces a smaller delivery flow at high pressure, and corresponds to a motor/pump combination. High-pressure and low-pressure feed lines, respectively, are provided for the high- and low-pressure delivery flows.

[0010] This proposed solution also takes up structural space and involves several mechanical components.

[0011] Starting from the state of the art mentioned at the beginning, the purpose of the present invention is to provide an oil supply device for hydraulic transmission control of an automatic transmission, in particular a change-under-load transmission with a demand-orientated oil supply stem, which takes up little structural space and can be produced at favourable cost. In addition, a method for operating the oil supply device according to the invention is to be described.

[0012] The objectives for an oil supply device are achieved by the characteristics of claim 1; the method for operating the oil supply device according to the invention is the object of claim 3. Other design features and advantageous embodiments emerge from the corresponding subordinate claims.

[0013] In this system, the oil circuit comprises a high-pressure circuit with high-pressure feed lines to the consumer devices and a low-pressure circuit with corresponding low-pressure feed lines.

[0014] According to the invention it is proposed to position, in the respective high-pressure feed lines to the valves of the consumer devices (clutches, variator discs, etc.), in each case an inlet aperture of small size, and to connect the low-pressure feed line between this inlet aperture and the corresponding valve. In this arrangement, the low-pressure feed line is separated from the high-pressure feed line by a spring-loaded one-way valve.

[0015] This arrangement or oil supply device according to the invention is operated as follows: when no gear shift operation is taking place, i.e., during steady state operation, only minimal high-pressure delivery flow passes through and, as a result, no pressure drop occurs at the inlet aperture so that high pressure prevails between the inlet aperture and the valve of the consumer device. The low-pressure circuit remains cut off from the high-pressure delivery flow by the closed one-way valve.

[0016] When a gear-shift element or adjustment device is actuated, for example the variator discs, the high pressure between the inlet aperture and the valve falls when the unpressurized additional gear-shift element volume is connected thereto, the one-way valve opens, and the gear-shift element is filled via the low-pressure circuit. During this, only a small amount of oil can flow out of the high-pressure circuit because of the small size of the inlet aperture.

[0017] At the end of the gear-shift element filling phase the delivery flow resumes very rapidly and, for example, a gear-shift element pressure is built up which closes the non-return valve. The subsequent main modulation of the gear-shift element pressure is effected by the high-pressure circuit.

[0018] The oil supply system, according to the invention, has the advantage that the two phases of “filling” and “modulation” are fed from separate circuits during a shifting operation or adjustment process.

[0019] In this way, the prerequisites are provided for implementing a demand-optimized dual-circuit system for the hydraulic control unit. The high-pressure circuit can be reduced to a minimum in relation to its delivery flow.

[0020] The structural space occupied by the proposed oil supply device and its production costs are very small. 

1. Oil supply device for the hydraulic transmission control of an automatic transmission, in particular a change-under-load transmission with demand-orientated oil supply, having a high-pressure circuit comprising high-pressure feed lines to the consumer devices and a low-pressure circuit with low-pressure feed lines to the consumer devices, characterized in that in each case the high-pressure feed lines to the consumer devices of the transmission system incorporate an inlet aperture of small size, the low-pressure feed line is connected between the said inlet aperture and the said consumer device, and the low-pressure feed line can be cut off from the high-pressure feed line by a one-way valve.
 2. Oil supply device according to claim 1, characterized in that the one-way valve is a spring-loaded one-way valve.
 3. Method for operating an oil supply device according to claim 1, characterized in that during steady state operation a minimal high-pressure delivery flow passes through, such that there is no pressure drop at the inlet aperture, so that high-pressure prevails between the inlet aperture and the valve of the consumer device and the low-pressure circuit consequently remains cut off from the high-pressure delivery flow by means of the closed one-way valve.
 4. Method according to claim 3, characterized in that when a consumer device is actuated, the high pressure between the inlet aperture and the consumer device falls because of the additional connection of the unpressurized gear-shift element volume, so that the one-way valve opens and the consumer device is filled via the low-pressure circuit, during which process very little oil flows out of the high-pressure circuit through the inlet aperture.
 5. Method according to claim 4, characterized in that after the end of the filling phase of the consumer device, the delivery flow resumes very rapidly, so that a pressure builds up which closes the one-way valve and the subsequent pressure modulation is effected by the high-pressure circuit. 